I have a fairly simple program below that is to utilize the shift cipher to encrypt an entered string. I have it working if I used a number when entering a value for k, but the requirement for the assignment is to use a Letter to denote 1-26 for the value of k. I can't seem to figure out what is wrong with my converChar function, if anyone has any thoughts please let me know..,I'm not a great programmer so I may have missed something small.

There's an error in your logic in the if statement of your convertChar() function. You should check the documentation for the strcmp() function and understand its return values, it has 3 different: greater than zero, less than zero, and zero. Also remember how the the if statement is decided, one you understand all these you'll find your mistake.

Other function that you may use instead of strcmp() and a sequential search, is strchr().